1. Field of the Invention
The present invention relates to a digital data transmitting/receiving system for transmitting motion image or picture data coded by the International Standard of ISO/IEC, MPEG-2 or the like for coding motion picture data with high efficiency. The present invention also relates to a digital data decoder device for decoding coded motion picture data and outputting it therefrom and a receiver for receiving displayed digital data. Incidentally, a description will be made below of an example in which the present invention is applied to a digital broadcast. However, the present invention is not necessarily limited to this. The present invention can be also applied to an example related to the transmission and reception of data such as data communications or the like in a similar mechanism.
2. Description of the Related Art
Due to an increase in the amount of digital motion image or picture data, high-efficiency coding means performs compression thereon to eliminate redundancy or the like and thereafter transmits or records the coded motion picture data, whereby the cost of transmission or recording can be reduced. As the high-efficiency coding means, there is well known an MPEG-2 system standardized by ISO/IEC/JTC1/SC29/WG11.
As to the coding based on the MPEG-2 system, respective frames of motion picture data are separated into an I frame (Intra Picture) coded without having a frame (reference frame) referred as a predicted value, a P frame (Predictive Picture) with only frames lying in the forward direction in display order as reference frames, and a B frame (Bidirectional Picture) with each frame lying in the forward direction and each frame lying in the backward direction as reference frames. Upon actual coding, two reference frames lying in the forward and backward directions are required to exist upon decoding the B frame, and the data coding is performed after the sequence of frames is skillfully interchanged.
While a decoder device successively decodes coded motion picture data transmitted in coding order, it is necessary to temporarily store the decoded data in a memory and re-arrange or sort the same in accordance with display order. It is also necessary to use decoded data of the I and P frames as reference data upon the subsequent decoding of B frame. The memory is required to certainly store motion picture data corresponding to two frames therein. The re-arrangement or sorting of the data in frame order is performed using each memory corresponding to the two frames. Since the data is coded in one frame unit, the frame data cannot be displayed simultaneously with decoding even in the case of the B frame when one frame is made up of two interlaced fields as in the case of a television signal. It is necessary to convert the frame data to field data sorted in the order of scanning lines. Even for this purpose, a memory corresponding to about one frame is required.
Further, image or picture signals compressed by the MPEG-2 system are classified into several categories. Special emphasis is placed on the two categories called a xe2x80x9cmain level (ML)xe2x80x9d and a xe2x80x9chigh level (HL)xe2x80x9d in particular from an application standpoint.
The main level corresponds to the NTSC system of horizontal 720 pixelsxc3x97vertical 480 scanning linesxc3x97frame frequency of 30 Hz and is adopted for a satellite digital broadcast. The high level corresponds to a high-definition image or picture expressed in horizontal 1920 pixelsxc3x97vertical 1080 scanning linesxc3x97frame frequency of 30 Hz. It has been determined to be adopted for a US ground wave digital broadcast intended to provide high picture-quality broadcasting services. The US ground wave digital broadcast has been introduced in the May 1997 issue, pp47-53 of Nikkei Microdevice, for example.
The capacity of a memory required to decode the coded motion picture data based on the MPEG-2 system is equivalent to one added with that for a coded image or pictorial data buffer for temporarily storing a coded image upon decoding in addition to the capacity corresponding to the three frames. The capacity of the coded image data buffer (VBV) corresponds to 1,835,008 bits in main level and 9,781,248 bits in high level. Even in the case of combinations of coding devices and decoder devices different in manufacturer, this capacitive value is determined by the MPEG-2 system as the required minimum capacity necessary to always maintain the assurance of suitable coding/decoding.
As also introduced in the May 1997 issue, pp47-53 of Nikkei Microdevice, the picture formats of the coded motion picture data range over many divergences. Thus, the display of decoded motion picture data corresponding to these all picture formats on a specific monitor needs to use a display device capable of displaying all these picture formats or utilize a format converting device between a decoder device and a display. The latter is advantageous to reduce the cost of the monitor.
Further, the satellite digital broadcast and the ground wave digital broadcast are not independent services for users who receive these broadcasts and enjoy the same. It is very natural that there is a demand that the users desire to enjoy even the conventional analog broadcast through the same television receiver. It is necessary to meet this demand.
An example of a device for decoding coded motion picture data, which can be used in a receiver for broadcast service in which picture formats of coded motion picture data have a variety of picture sizes as in the US ground wave digital broadcast, has been disclosed in Japanese Patent Application Laid-Open No. Hei 8-205161. This example is a proposal wherein a high-definition motion picture (HD:High Definition) is decoded while being downsampled to a standard motion picture (SD: Standard Definition) corresponding to the same format as the analog broadcast, thereby facilitating provisions to a plurality of picture formats.
However, the present example has a problem in that the high-definition picture data is merely outputted as the standard picture data and hence the users cannot enjoy a precious high picture-quality broadcast. Further, the example also contains no mentions of a configuration capable of receiving the analog broadcast simultaneously.
An object of the present invention is to solve the above problems, facilitate provisions to broadcasted variety of picture formats and realize simultaneous reception of an analog broadcast.
According to one aspect of the invention, for achieving the above object, the present invention comprises means for decoding motion picture data used in a digital broadcast, memory means for storing the decoded motion picture data therein, first on-screen data multiplexing means for mixing the decoded motion picture data with first on-screen data, first picture format converting means for converting the first on-screen data-mixed motion picture data into format form, and second on-screen data multiplexing means for mixing the format-converted motion picture data with second graphics data, whereby the second on-screen data-mixed motion picture data is outputted. Thus, the motion picture data used in the digital broadcast can be outputted in an arbitrary picture format so that a high picture-quality display can be done. The on-screen data allows the high picture-quality display too. Further, the present invention includes second picture format converting means. The output of second format-converted motion picture data as an output for a recording device from the second picture format converting means makes it possible to use the conventional analog broadcasting recording device.
Further, the present invention includes picture data capturing means for inputting motion picture data used in an analog broadcast therein, and motion picture data memory storing means for allowing the memory means to store the motion picture data used in the analog broadcast. By applying the first picture format converting means even to the motion picture data used in the analog broadcast, the motion picture data can be outputted or displayed without drawing a distinction between the analog broadcast and the digital broadcast.
According to the present invention, as has been described above, high-definition motion picture data can be displayed while remaining high in image quality as the high-definition motion picture data. Further, even if the data is broadcasted in the form of a plurality of image or picture formats, their display picture formats are converted to the same. It is therefore possible to achieve a reduction in the cost of a monitoring device. Since standard motion picture data can be outputted simultaneously with the display motion picture data in addition to the display motion picture data, the conventional analog broadcasting recording device can be also utilized. Further, since the conventional analog broadcast can be also converted to a high-definition motion picture format and displayed in this form, even the conventional analog broadcast can be displayed with high picture quality, described specifically, an easy-to-see screen from which scanning line interference like line flicker (corresponding to such a phenomenon that fine points are flickering) can be provided. Moreover, since data can be displayed in picture-in-picture form or graphics data can be on-screen displayed, a table for an electronic program guide can be displayed. According to the electronic program guide, a cursor of a remote controller is set to or aligned with a program to thereby make it possible to choose a channel and make a recording reservation. The provision of two-system OSDs allows graphics to be displayed on TV but unrecorded on VTR as well as superimposition of graphics on both the TV display and VTR recording, thus making it possible to implement an easy-to-understand user interface.